// ====== scroll top js
function scrollTo(element, to = 0, duration = 500) {
  const start = element.scrollTop;
  const change = to - start;
  const increment = 20;
  let currentTime = 0;

  const animateScroll = () => {
    currentTime += increment;

    const val = Math.easeInOutQuad(currentTime, start, change, duration);

    element.scrollTop = val;

    if (currentTime < duration) {
      setTimeout(animateScroll, increment);
    }
  };

  animateScroll();
}

Math.easeInOutQuad = function (t, b, c, d) {
  t /= d / 2;
  if (t < 1) return (c / 2) * t * t + b;
  t--;
  return (-c / 2) * (t * (t - 2) - 1) + b;
};

const backToTopBtn = document.querySelector(".back-to-top");
if (backToTopBtn) {
  backToTopBtn.onclick = () => { scrollTo(document.documentElement); };
}